Document how to run simulation tests for new contributors

We weirdly lack documentation for how to actually test code. It'd be good to definitely highlight cmake+ctest as the preferred workflow, but mentioning how to directly run a `./fdbserver -r simulation -b on -s 123 -f test.txt` test would be good.

Start by locating the contributor or testing documentation and existing CMake/CTest instructions. Document the preferred CMake plus CTest workflow and the direct fdbserver entry point using `./fdbserver -r simulation -b on -s 123 -f test.txt`; done means a new contributor can run both workflows from the documentation.

Written by the indexing model from the issue text.